After getting into debt with her energy supplier, 19-year-old Laura Coyle from Preston has been told she has to have a pre-payment meter to help pay off the debt. But the move will mean she will join hundreds of thousands of others paying up to £80 a year more for her gas and electricity. According to the children's charity Barnardo's that's the extra cost of using meters compared to paying by direct debit.

The problem is that the only people forced to use the meters are those struggling with debt – the same vulnerable low-income families who need most help with paying their bills.

Laura lives with her partner, Sam, in Preston. Until now the family have been paying £60 a month on an online British Gas tariff for gas and electricity – but were shocked to be told that they actually owe the firm £600.

"There's just no way we can afford £600 on top of the monthly bills we're paying," Laura said. "We've now been told we've got to start on a pre-payment meter in November in order to pay off the debt."

The extra cost of using a meter will add to the family's financial woes. But while they are struggling, they are just about managing to stay afloat thanks to part-time work and benefits but also because of support from Barnardo's' Moving On service in Preston.

"Jackson's cot broke the other week, and Barnardo's are going to help get us a new one. We couldn't afford to replace it otherwise – we just don't have that kind of money," Laura admits.

The charity's chief executive Anne Marie Carrie said: "Many of the families Barnardo's works with are bearing the brunt of companies' unfair tariffs because they are using pre-payment meters to pay off their debt and to pay for gas and electricity. Effectively these families are being penalised by their payment method at a time when they need the most financial help."

She said energy companies have a moral duty to behave responsibly by ensuring the poorest families are on the lowest tariffs available and prices for pre-payment meters are brought down to the same rates as online tariffs.

"Furthermore, we would urge the Government to tackle the issue of fuel poverty by the root, by bringing forward the requirement on landlords to make their properties energy-efficient for tenants," said Ms Carrie.

Laura says her family's real problem is the house they rent. "There are gaps under the windows and a big slit in the front door where the heat escapes," she said. "We're always juggling payments because of the energy bills. I've just switched supermarkets from Asda to Iceland because the food I get is ever so slightly cheaper there."

The young mum is angered by the fact that British Gas never told her that there were better deals available. "When you're struggling to get by, every penny counts, but with the energy tariffs I just don't know which one we should have been on.

"I've just had another provider get in touch saying they could have offered us a cheaper tariff. But now we're in debt I can't even change provider."

Ms Carrie said the Government must solve the problem of the poorest people being charged the most for energy. "If we're serious about tackling child poverty then we need to get serious about tackling fuel poverty, too.

"Families should never have to choose between whether to heat their homes or put food on the table for their children."